I didn't spend a lot of time playing it, but it seems pretty well-done. The two issues that stand out to me in particular are that the card names are confusing, and that there's no way to tell which cards you've already selected.

Perhaps you could try and render actual hearts, diamonds, trees, and spades, rather than using the characters H D C and S. This could be accomplished with multiple Text( commands, and maybe some Pxl-Ons and Offs.

The other issue could be fixed easily just by underlining selected cards.

Good luck making the AI - I forsee the AI version being much more fun/useful than the current multiplayer incarnation.

I think you made a slight mistake, your site says the size is 9700 KB…that would never fit! i assume you meant 9700 bytes? Well never mind it is a slight problem compared to the amazingness factor of this game! Also about AI implentation, I think you could do this relatively easily…just make a subprogram, don't try to teach AI all the possibility's but give it the RULES (these can be quite easily defined in simple AND/OR/XOR/NAND/NOR etc gates) Also a tactic of mine for AI is not to try letting it win but block the other (human) player…(altough that implents easier in a connect4 game then chinese poker i guess…)